Well, I've got a trip planned up to Cuba in February (Isla da Juventud) and so I have just started researching.
The general opinion I got from everybody I talked to was that I should take all my own gear and my save-a-dive kit as available rental gear is extremely variable from non-existant to tolerable.
This is no problem as my wife and I are both fully equipped including safety gear and I normally take in the dive-bag, a spare fin strap, spare mask strap, spare spg, spare 2nd stage, o-rings, spare bulbs for the dive lights etc.
I also just bought myself a cheap 3mm full coverage wetsuit for this trip, because of the water temperatures around 26C. Normally I dive in much colder water (using 5mm plus full coverage) or much warmer (using 3mm shorty or lycra skin).
The real doubt I have at the moment is what to take in the way of cash. Apparently credit cards are not widely accepted and US$ are now complicated due to the recent laws in Cuba, so it looks like it has to be Euro notes.
Sea life should be typical Caribbean with some spectacular coral formations at depth (40 - 50m).
PS. I just remembered. Everybody warned me against excess weight for baggage. Apparently they regularly apply this when travelling back from Cuba.